This study aimed to evaluate the changes produced by the selective logging of forests on northwest of Mato Grosso (Juruena), on the stock and input of coarse woody debris (CWD), at three ages after logging (2, 6-7 and 11-12 years). Measurements included: diameter and the length of the stems; the state of decomposition of ali the dead trunks (0 > 10 cm); and, the probable cause of the mortality of trees contained in 16 plots of 40 x 125 m. The mean stocks of CWD were 33.7 Mg ha-1 in the undisturbed forest and of 20.6, 19.9 and 26.4 Mg ha-1 in the logged forests (2, 6-7 and 11-12 years, respectively). The main change in result of the selective logging was observed on the CWD with diameter of 2-10 cm, which showed a strong increase in the stock (105%) and in the volume (37%) of dead wood. ín the selectively logged forests, the fine woody litter (0 2-10 cm) fraction represented 42-56% of the total volume of CWD, and 15-16% of the stock; however, It stores 29-34% of the total N in CWD, 35-40% of the P, 18-20% of the K, 37-42% of Ca and 30-35% of the Mg. Overall, the selective logging generated an increase of 54-109% in the stock of nutrients in such residues, compared to the undisturbed forest. The biggest annual inputs of CWD were found in the undisturbed forest (5.7 Mg ha-1 year-1) and in the forest with 11-12 years after logging (5.3 Mg ha-1 year-1), while the plots 2 and 6-7 years old after logging showed inputs of only 1.1 and 2.8 Mg ha-1 year-1, respectively. The fine woody litter (0 > 2-10 cm) represented 8-9% of the annual input of CWD in the undisturbed forest and of the logged plots with 11-12 years, and for 34% and 40% in the plots with 2 years and 6-7 years after logging, respectively. The biggest stock and input of CWD of palms occurred in the disturbed forests, with an increase of 120-340% in the mortality of palms. There weren't significant changes in the density of soil (0-10 cm) and in the stock of organic C, N and K in the soil (0-20 cm) in result of the logging. However, selective logging caused significant increase on the stocks of available-P, Ca and Mg in the plots logged more recentiy (2 and 6-7 years). Zones with high soil carbon and nutrient concentrations had been identified under decomposing plant residues, with large differences in concentrations compared to the average of the plots' increases of 174% for C, 167% for N, 202% for avail-P, 140% for K, 1129% for Ca and 403% for Mg. Density of the dead wood (0.20-0.70 Mg m-3) showed negativa correlation with the intensity of contact of the trunks with the soil, and decreased with the time of decomposition. Thus, the main changes induced by the selective logging were: (i) high mortality of palms; (ii) a strong increase in the stock and the input of CWD with 0 2-10 cm; and (iii) the formation of zones with high concentrations of available nutrients in the soil, derived from the decomposition of the accumulated wood residues, especially of the finest fraction (with 0 2-10 cm), because they showed higher concentrations of nutrients.
|
